Calculation of the end-region field of a.c. machines

The rapid increase in electric loadings of turboalternators has demanded improved methods of predicting the end-zone field distribution. The paper describes an analytical method for calculating the flux distribution in the end zone of a.c. machines based on the solution of Laplace's equation for the scalar magnetic potential. All end-zone boundaries are taken into account, although simplifications of shape and of magnetic behaviour are made. Stator end turns are assumed to lie on a cylindrical surface. The case of an infinitely permeable core end surface is given special consideration, and equations are derived for the field components. The equations are in the form of double Fourier or Fourier-Bessel series, and convergence is discussed. An equation is also derived for stator-end-winding inductance.The validity of the equations has been checked by measurements on a simple model machine wound with a single coil per pole, which is the basic element in the analytical work. Agreement is encouraging. Calculated results for a large turboalternator are given. Some possible improvements in the method are briefly discussed.

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